This invention relates to a gas spring and, particularly, to a gas spring of the type wherein it is possible to fill gas into the gas spring safely and reliably during manufacturing or repairing processes, and which has a simple construction.
Conventional gas springs comprise a cylinder, a piston working in the cylinder, a piston rod secured to the piston at one end thereof and extending out through one end of the cylinder, and a rod guide disposed at one end of the cylinder for slidably guiding the piston rod therethrough.
One prior art gas spring of the aforementioned kind comprises, such as shown in Japanese patent disclosure (Kokai Koho) No. 52-70416, a seal ring being disposed adjacent to and inwards of the rod guide for sealingly engaging the piston rod and the cylinder, and a reduced diameter portion being formed on the piston rod, whereby when the seal ring is located radially outwards of the reduced diameter portion a gas passage is formed between the seal ring and the piston rod thus enabling gas under pressure to be filled into the cylinder at a high speed.
In such case when gas under pressure is filled into the cylinder the seal ring and the rod guide have sometimes been displaced inwardly of the cylinder or towards the piston, depending on the pressure and velocity of the gas being filled into the cylinder since, in particular, in the initial stage of the gas filling process, pressure in the cylinder is substantially lower than that of the compressed gas, and the gas filling passage has sometimes been restricted or, in the extreme case, closed due to displacement of the seal ring passing over the reduced diameter portion to engage with a large diameter portion of the piston rod. Therefore, there is problems such that compressed gas cannot be filled reliably into the cylinder.